1. Field of Invention
The invention relates to a zoom lens for digital image capturing devices, such as digital static cameras and digital video cameras. In particular, it relates to a zoom lens with a more compact structure, a higher picture quality, a high resolution, and a wider angle. The disclosed zoom lens further has the properties of a high relative illumination and a small incident angle. This is particularly suitable for devices capturing digital images, such as CCD.
2. Related Art
In recent years, the research and production of zoom lenses have made a great progress. Besides advances in their performance, the zoom lenses are also designed for the convenience of users. Manufacturers make all efforts to lower the lens production cost and decrease the lens set length in order to enhance their competitive power. In particular, the zoom lenses for the digital static camera (DSC) and the digital video camera (DVC) have the greatest market potential.
In the prior art such as the U.S. Pat. No. 6,611,386, JP Pub. No. 2003-5072, U.S. Pat. No. 6,597,513, and U.S. Pat. No. 6,308,011, people always try to achieve minimizing the lens sets by reducing the number of lenses. However, they cannot provide the desired properties such as large F/#, large field of view (FOV), the zoom ratio, and the number of lenses. Take F/# as an example, its usual value of a normal DSC lens set is 2.8, whereas that of the DVC lens set is required to be 1.8. One thus sees that there is room to improve.
The U.S. Pat. No. 6,611,386 adopts the design of six lens pieces and can only reach: zoom ratio=2.5, F/#=2.8, and FOV (2ω)=63 degrees. The JP Pub. No. 2003-5072 adopts the design of seven lens pieces, achieving: zoom ratio=3, F/#=2.5, and the largest FOV (2ω)=65 degrees. The U.S. Pat. No. 6,597,513 also adopts the seven-piece design, with the zoom ratio=2.5˜4, F/#=2.8, and the largest FOV (2ω)=60 degrees. The U.S. Pat. No. 6,308,011 also adopts the seven-piece design, with the zoom ratio=3, F/#=2.8, and the largest FOV (2ω)=64 degrees.
Therefore, it is necessary to provide a small zoom lens that has the properties of high brightness, wide angle, and homogeneity.